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Wednesday, Mar. 20. QUIZ #3 IN CLASS Assignments: Article Outline #1 (due today) Mini-Project #1 - Part 2 (due Wed. Mar. 26). Venus from the Ground:. Thought Question:. - PowerPoint PPT Presentation
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The Jovian PlanetsCOMPARISON OF SIZES:
Gas Giants Ice Giants
1. Distance from the Sun
2. Size & Mass
3. Chemical Composition
4. Rotation
5. Moons & Rings
…and what do extrasolar planets tell us?
Main differences between terrestrial and jovian planets:
1. Jovian planets follow circular orbits farther from Sun than terrestrial planets
• outermost terrestrial planet (Mars): 1.5 AU
• innermost Jovian planet (Jupiter): 5.2 AU
COMPARE ORBITS
jovian planets probably formed where icy material could condense
Orbits of Extrasolar Planets
• most detected planets have orbits smaller than Jupiter’s
• planets at greater distances are harder to detect…
star wobbles less wobble changes slowly “observational bias”
2. Jovian planets bigger and more massive than terrestrial planets
• 4 to 11 Earth’s size
• Each has more mass than all terrestrial planets
• Jupiter has more mass than ALL planets
More raw material available (ices, hydrogen and helium gases, as well as rock) for jovian planets
3. Jovian planets have different composition than terrestrial planets
ATMOSPHERES:• spectrums reveal mostly hydrogen compoundsDENSITY:• low densities require mostly hydrogen and helium
methane responsible for bluish colors
Jupiter
Clouds:
colors from materials condensing at different depths:
ammonia(NH3)
ammonium hydrosulfide (NH4SH),
water (H2O), DEEPEST
SHALLOWEST
Saturn
Uranus
Clouds -
• Methane (CH4) absorbs red light
Neptune“Great Dark Spot” – now gone
methane (CH4) ice clouds
Thought Question:How does the escape velocity for Saturn
(mass: 95 Mearth, radius 9.5 Rearth), compare to Earth’s?
A. about 20 times larger
B. about 20 times smaller
C. about 10 times larger
D. about 10 times smaller
E. about 3 times larger
F. about 3 times smaller
Thought Question:How does Uranus’ (about 4 Earth radii, 15
Earth masses) density compare to Jupiter’s (about 11 Earth radii, 318 Earth masses)?
(Enter the ratio rounded to one decimal place.)
Interiors• Jupiter, Saturn: probably formed first and captured more H and He
(closer to Sun, icy planetesimals and gas were common)
compressed metallic hydrogen probably causes large magnetic fields
• Uranus, Neptune: mostly compressed “icy” material
Extrasolar Planet Densitiesjovian planets in solar system: 0.7 - 1.7 g / cm3
jovian-mass extrasolar planets have wide range in densities: 0.1 - 9 g / cm3!
4. Jovian planets rotate faster than terrestrial planets
Earth: 24 hours
Jupiter: 9 hours 50 min (fastest)
Uranus: 17 hours 14 min (slowest)
jovian planets got a lot of angular momentum from gases they pulled in
Thought Question:What should happen to a rapidly spinning
planet if it is mostly made of materials that aren’t solid?
A. It will bulge outward at its equator.
B. It will bulge outward at its poles (like a football).
C. It will expand in all directions.
D. It will pull inward all over.
E. Nothing really - it will just spin normally.
Oblateness• “flattening” caused by planet’s rotation – shape is not a sphere• The more of the interior that is fluid, the more it will bulge at its
equator when it rotates
Example: tossing pizza
5. Jovian planets have many moons and rings
COMPARE
• Terrestrial planets:
Earth: 1 big moonMars: 2 asteroid-
sized moons
• Jovian planets:Many asteroid-
sized moons, some larger
Mostly ice, rock, or combination
5. Jovian planets have many moons and rings
• No terrestrial planets have rings
• All Jovian planets have rings
visibility of rings depend on how reflective they are
Light Waves… caused by accelerating electrial charges
wavelength (λ): distance between successive wave crests
different colors have different wavelengths:
frequency (f): number of wave crests that pass per second
units: number per second, or Hertz (Hz)
for sound waves, frequency = PITCH
speed of light (c):
WAVELENGTHWAVELENGTH
BLUERED
700 nm 400 nm
The Electromagnetic Spectrum
• visible light is just a small part of the entire spectrum:
increasing
f decreasing
Thought Question:What wavelength will radio waves from station
“90 FM” have? (FM station frequencies are given in mega-Hertz, or 106 Hz.)
(Enter the answer in m to two significant digits.)
Light Wavesenergy (E): higher frequency larger energy
WAVELENGTHWAVELENGTH
BLUERED
Thought Question:
SpectrumSPECTRUM: a way of describing a MIXTURE of light:
how intense are different colors?
Roughly equal mixture of colors appears WHITE:
LIG
HT
INTEN
SIT
Y
WAVELENGTHV I B G Y O R
LIG
HT
INTEN
SIT
Y
WAVELENGTHV I B G Y O R
Unbalanced mixtures are tinted by most intense colors:
Observing a SpectrumSELECT SPECIFIC
WAVELENGTH RANGES (FILTERS)
SPLIT LIGHT BY WAVELENGTH
(PRISMS, CDs)
greyscale (lighter = more intense)
Thought Question:If I project dots of red and green light on the
screen, what will you see where they overlap?
A. A yellow dot
B. A brown dot
C. A blue dot
D. A black dot
E. A white dot
If I project dots of blue, red, and green light on the screen, what will you see where they overlap?
The Importance of SpectrumsAtoms of each element …
absorb and emit unique combinations of colors AND work the same way across the universe
Spectrums can be used to:
identify chemicals
measure temperature
measure speeds
ABSORPTION
The Ring Nebula
1 LIGHT-YEAR
EMISSION
THERMAL RADIATION
Kinds of Spectrum
INTEN
SIT
Y
WAVELENGTHV I B G Y O R
CONTINUOUS
INTEN
SIT
Y ABSORPTION LINE
INTEN
SIT
YEMISSION LINE
400 nm 700 nm
Kinds of SpectrumCONTINUOUS: hot, opaque materials emit thermal radiation
INTEN
SIT
Y
WAVELENGTHV I B G Y O R
EXAMPLE GRAPH:
examples: light bulbs, you, stars (sort of)
Jupiter’s Moon Io
Jupiter’s Moon Io
Star Colors
Thermal Radiationhot, opaque objects radiate light in a way that depends only on
temperature• as T increases: light of all wavelengths gets brighter wavelength of most intense light gets shorter (bluer)
BLACK
(no visible light)
RED ORANGE YELLOW WHITE
WHAT WE SEE BY EYE:
Thermal RadiationStefan-Boltzmann Law: brightness at surface of hot object (also called flux)
(energy released per second per area)
FOR SAME AREA, HOT SURFACE RELEASES LIGHT FASTER
ALL COLORS GET MORE INTENSE
(a constant)
Thermal Radiation• thermal radiation is released at all
wavelengths, but…
Wien’s Law: most intense light is released at this wavelength:
HOTTER=BLUER
Sun:
Blackbody Applet
Temperature
INFRARED VIEWS ON EARTH (FALSE COLOR)
Police Video
SATURN (FALSE COLOR:
RED = INFRARED)
ULTRAVIOLET LIGHT SOURCES ON EARTH
Thought Question:The hottest stars can be more than ten times hotter than
the Sun at their surfaces. How much brighter (energy released per m2 per sec) would the surface of such a star be compared to the Sun?
What would the peak wavelength of such a star be (in nm) if the Sun’s peak is at around 500 nm?
Star Luminosity
Stars release THERMAL RADIATION: brightness of each piece of surface
only depends on temperature
Apply Stefan-Boltzmann Law:
flux from each piece of star’s surface
star’s surface area
• luminosity (L): total amount of energy released per time
units: Watt (W): 1 W = 1 J / s property of a star: its “power”
Thought Question:The graph below shows the blackbody
spectra for three different stars. Which of the stars is at the highest temperature?
A. Star A
B. Star B
C. Star C
Jupiter’s Moon Io
Thought QuestionWhat kind of spectrum would you see if you were
looking in the direction shown by the arrow?
A. continuous (thermal radiation) spectrum
B. absorption line spectrum
C. emission line spectrum
transparent gas cloud
star
Types of Spectrumtransparent gas
cloud
(atoms can absorb specific wavelengths
of light AND emit the same
wavelengths)
star
(source of thermal radiation
– frequent collisions
between electric charges)
ABSORPTION
THERMAL RADIATION
EMISSION
WHAT YOU SEE:
Thought Question:
When I pass a jug of clear blue liquid in front of the light bulb, what will happen?
A. The jug will make the violet, blue, and green light more intense.
B. The jug will make the yellow, orange, and red light more intense.
C. The jug will remove most of the violet, blue, and green light.
D. The jug will remove most of the yellow, orange, and red light.
Kinds of SpectrumABSORPTION LINE: transparent material in front of hotter opaque material
INTEN
SIT
Y
WAVELENGTHV I B G Y O R
EXAMPLE GRAPH:
light is removed by cloud
examples: seeing stars through gas (like an atmosphere)
sodium
hydrogen
magnesium
iron
Sun
sodium
hydrogen
magnesium
iron
Arcturus
ORION NEBULA
(about 24 light-years across)
Kinds of SpectrumEMISSION LINE: hot transparent material in front of cool background
INTEN
SIT
Y
WAVELENGTHV I B G Y O R
EXAMPLE GRAPH:
light is released by cloud
examples: street lamps, fluorescent bulbs, interstellar gas clouds
Thought Question:
Which of the following patterns most closely resembles the pattern of lines you saw in the spectrum?
A.
B.
C.
D.
AtomsNUCLEUS: contains almost all of an atom’s mass
protons: positively-charged particles
neutrons: particles with no charge
ELECTRON CLOUD: electrical force keeps electrons near nucleus
electrons: negatively-charged particles
HYDROGEN HELIUM
More protons in nucleus means:
stronger electrical force
electrons more tightly bound to atom (on average)
Absorbing Light• Electron only absorbs light with correct amount of energy to move it to an allowed distance from nucleus
GROUND STATE-6
-3
-1
ELECTRON
ENERGY LEVELS:
WHAT HAPPENS IN ATOM:
electron moves farther from nucleus
2 UNITS OF ENERGY ABSORBED
Emitting Light• Electron releases exact amount of energy needed to drop it to
a smaller allowed distance from nucleus
GROUND STATE-6
-3
-1
ELECTRONENERGY LEVELS
WHAT HAPPENS IN ATOM:
electron moves closer to nucleus
3 UNITS OF ENERGY RELEASED
Energy Levels
allowednot allowed
E1
E2
E3
E4
E=0
electrons in atoms are only allowed to:• have specific amounts of total
energy• transition to other allowed energy
levels OR off the atom absorbed light will have characteristic E and :
n = 1
n = 2
n = 3n = 4
Thought Question:The electrons in an atom can be in the energy levels shown
below. If an electron is in the ground state (the level with an energy of -9 units), how many units of energy can the electron absorb and still remain attached to the atom?
(Enter ALL possible correct answers as one number, then hit send.)
Hydrogen:the simplest atom…
Balmer lines:
-13.6 eV
-3.4 eV
-1.5 eV
-0.8 eV
0 eV
E
nlo = 2nhi =3,4,5,…
nlo = 1nhi =2,3,4,…
Review QuestionIn what order do we think the following things
appeared in the solar system as it formed?A. snowflakes and dirt particlesB. Earth-sized protoplanetsC. rotating disk of gasD. asteroids and cometsE. large cloud of gas
Review Question:The choices below describe 4 hypothetical planets. Which planet
surface would you expect to be least crowded with impact craters? (Assume they orbit a star just like the Sun and are the same age as the planets in our solar system.)
Size Distance from Sun Rotation Rate
A. same as Venus same as Mars every 25 hours
B. same as Moon same as Mars every 10 days
C. same as Mars same as Earth every 10 hours
D. twice Earth size same as Mercury every 6 months
Review QuestionThe image below shows a picture of Mare Imbrium
on the Moon. Put the following features in order from oldest to youngest: A) Imbrium lava, B) Sinus Iridium, C) the Apennine mountains?
Review QuestionIf you decreased the temperature of a star, would the
following A) increase, B) decrease, or C) stay the same?
the intensity of the color red? the intensity of the color blue? the wavelength of the most intense color?